This application is the U.S. National Phase under 35 U.S.C. xc2xa7371 of International Application PCT/JP00/00598, filed Feb. 3, 2000, which claims priority to Japanese Patent Application No. 1999-31573, filed Feb. 9, 1999. The International Application was not published under PCT Article 21(2) in English.
The present invention relates to heat shrinkable films whose heat shrinkage in the main orientation direction is small in a low temperature range but large in a high temperature range, in particular the heat shrinkable films useful as labels.
It is a common practice to apply heat shrinkable films (labels) bearing printing on the internal surface to containers such as plastic containers, for exhibiting product names, instructions for use and other information, or for decorative purposes. Basic properties required of such films include transparency, gloss and firmness. Studies have been made on films comprising polystyrene resins or polyester resins to find a material satisfying the requirements (for example, Japanese Unexamined Patent Publications Nos. 272182/1997, 25349/1982 and 122152/1994).
Japanese Unexamined Patent Publication No. 272182/1997 discloses a heat shrinkable multi-layer film comprising inner and outer layers of a copolymer resin containing 2 to 50 wt. % of a polystyrene and 98 to 50 wt. % of a styrene-butadiene block copolymer with a styrene content of 65 to 90 wt. % and a butadiene content of 10 to 35 wt. %, and an intermediate layer of a polystyrene resin. The disclosed film has heat shrinking properties not possessed by a single-layer film, and is good in natural shrinking properties and firmness.
Japanese Unexamined Patent Publication No. 25349/1982 discloses a heat shrinkable film made of a mixture of 2 to 40 parts by weight of a polystyrene and 100 parts by weight of a styrene-butadiene block copolymer of the formula (S-B)n-S (wherein S is a styrene block, B is a butadiene block and n is an integer of 2 or more) with a styrene content of 70 to 93 wt. % and a butadiene content of 30 to 7 wt. %. The film, when used in combination with a styrene container, is advantageous from the viewpoint of recycling.
Japanese Unexamined Patent Publication No. 122152/1994 discloses a label made of a mixture of at least two polymers selected from the group consisting of polyethylene terephthalates synthesized from terephthalic acid or its derivative and a glycol component, copolyesters synthesized from terephthalic acid or its derivative and ethylene glycol having 1,4-cyclohexane dimethanol introduced therein, and copolymers synthesized from terephthalic acid or its derivative, isophthalic acid or its derivative and a glycol component. The heat shrinkage-temperature curve of the label has a sharp rise between 60xc2x0 C. and 95xc2x0 C.
However, the films disclosed in Japanese Unexamined Patent Publications Nos. 272182/1997 and 122152/1994 have a small heat shrinkage in a high temperature range, and thus have the problem that when they are applied by heat shrinking to a bottle having a neck diameter much smaller than the body diameter (i.e., a bottle with a high degree of taper) to wrap the bottle from the body portion to the neck portion or to the cap top surface, the films do not sufficiently shrink at the neck portion or the cap top surface, failing to achieve good finished conditions.
An object of the present invention is to provide a heat shrinkable film suitable for applying by heat shrinking to a bottle having a neck diameter much smaller than the body diameter to wrap the bottle from the body portion to the neck portion, from the body portion to the cap top surface, from the bottom portion to the neck portion, or from the bottom portion to the cap top surface, the heat shrinkable film preferably having a small natural shrinkage in the main orientation direction.